saying listen, we have emergency vehicles coming to you. About a minute passes and then the pilot gets back on the radio, he stayed in the cockpit talking to the tower, he did not evacuate immediately as passengers were evacuated by flight attendants. David kerley on the fast-moving investigation. As we were on the air late this afternoon, many eyewitnesses describing what they saw, the angle of the plane, likely why the tower knew there was trouble. The eyewitnesses describing, flame, rescue efforts that were quickly under way and linzie janis with their stories. Reporter: Within 40 minutes of the crash landing, a tweet from someone on board. An executive vice president at samsung electronics, david eun, says "i just crash landed at sfo. Tail ripped off. Most everybody seems fine. I'm okay. Surreal." S that eyewitnesses like stephanie report the asiana flight was coming in, saying they knew immediately something was wrong. I noticed the angle was wrong, that it was tilted too far back and I could tell that something was going to happen and then the angle, didn't manage to straighten out before hitting the runway so the tail of the plane hit the runway and it was -- it cartwheeled and spun and tail broke off and it looked like the plane had completely broken apart. Reporter: Another account, almost identical. The plane looked like -- i noticed the nose was very high, higher than usual. That's odd. But I was like, the pilot knows what he's doing. All of the sudden the tail hit. Flames came out and started to turn a cartwheel and I couldn't tell if it slid or not and also, it was in flames. Reporter: Danielle wells tweets this picture showing billowing smoke, saying "literally just witnessed a plane crash from start to finish. I cannot stop crying. I can't believe this." It was too much for some to watch. We saw the plane crash and we saw the rescue squads come out but we were so just overwhelmed that we didn't want to continue watching. Reporter: And the samsung executive tweeted about an hour ago, david eun, saying went through customs, adrenaline rush subsiding, trying to process all this. So many survivors and eyewitnesses saw this echoing one another. I want to bring in our aviation consultant john nance on the phone, he's been with us all day long. I want to ask you what we heard so many talk about as this unfo unfolded, the angle of the plane, the tail landing first. You were tellinging me this is unprecedented? Reporter: It is. And tells me the airplane was too low and too slow. Why we don't know, it echos very much the only other accident with the 777 in 2008 in britain when they lost power. They didn't have enough power to make the runway. In this case they didn't have an edge to hit like they did here. We're looking at pieces of the runway, parts of the wing, stabilization equipment that helps the plane land, tearing off the plane there. I want to ask you about something else, we saw the charred fuselage, nothing left of the roof of the plane from the thirst throw three-quarters of the way back, what does this tell but tremendous flight crew and training to get so many of the passengers off? It tells me how much progress we made in the last 50 years. Basically, things don't burn easily inside the airplanes,

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